Black leaf tea is traditionally produced by oxidising and drying freshly plucked green tea leaves. The method of preparing such teas is well known to those skilled in the art. Generally, to prepare black leaf tea, fresh green leaves of the plant Camellia sinensis are withered (subjected to mild drying), comminuted or macerated, fermented (in which process enzymes in the tea leaf use atmospheric oxygen to oxidise various substrates to produce brown-coloured products) and then fired (to dry the tea leaves).
The withering process, which is sometimes omitted, allows certain chemical and biochemical changes to occur and also the moisture content of the leaves is brought down from 90% to 50-70%. Biochemical/chemical changes taking place during withering, increase the yield of the volatile flavour compounds in tea.
The disruption of the cellular integrity of leaf during the maceration step allows oxidation of catechins by enzymes such as polyphenol oxidase that results in the development of colour and aroma molecules.
Phenylacetaldehyde and benzaldehyde are the major aroma components and are formed during the fermentation stage. During the process of fermentation, the quinones formed from catechins by the action of enzyme polyphenol oxidases/peroxidases convert phenylalanine into phenyl acetaldehyde. Phenyl acetaldehyde imparts a floral aroma whereas benzaldehyde has a sweet almond like aroma. Apart from phenylacetaldehyde and benzaldehyde, the terpenoids are also important in imparting floral aroma to tea.
Jasmonic acid and its derivatives such as methyl jasmonate and dihydro jasmonate are known to induce senescence in plants and also mimic wound signal. However, it has now been found that treating tea leaves post plucking with these chemicals significantly enhances the aroma of tea.